Integration of backside heat spreader for thermal management

ABSTRACT

A microelectronic device includes semiconductor device with a component at a front surface of the semiconductor device and a backside heat spreader layer on a back surface of the semiconductor device. The backside heat spreader layer is 100 nanometers to 3 microns thick, has an in-plane thermal conductivity of at least 150 watts/meter-° K, and an electrical resistivity less than 100 micro-ohm-centimeters.

FIELD OF THE INVENTION

This invention relates to the field of microelectronic devices. Moreparticularly, this invention relates to thermal management structures inmicroelectronic devices.

BACKGROUND OF THE INVENTION

Semiconductor devices with localized heat generating componentsexperience hot spots which cause reduced reliability. Removing the heatwhile maintaining desired costs and structural form factors has beenproblematic.

SUMMARY OF THE INVENTION

The following presents a simplified summary in order to provide a basicunderstanding of one or more aspects of the invention. This summary isnot an extensive overview of the invention, and is neither intended toidentify key or critical elements of the invention, nor to delineate thescope thereof. Rather, the primary purpose of the summary is to presentsome concepts of the invention in a simplified form as a prelude to amore detailed description that is presented later.

A microelectronic device includes semiconductor device with a componentat a front surface of the semiconductor device and a backside heatspreader layer on a back surface of the semiconductor device. Thebackside heat spreader layer is 100 nanometers to 3 microns thick, hasan in-plane thermal conductivity of at least 150 watts/meter-° K, and anelectrical resistivity less than 100 micro-ohm-centimeters.

DESCRIPTION OF THE VIEWS OF THE DRAWING

FIG. 1 is a cross section of an example microelectronic device with abackside heat spreader layer.

FIG. 2 is a cross section of another example microelectronic device witha backside heat spreader layer.

FIG. 3 is a cross section of another example microelectronic device witha backside heat spreader layer.

FIG. 4 is a cross section of another example microelectronic device witha backside heat spreader layer.

FIG. 5A through FIG. 5C depict an example process of formingmicroelectronic devices with backside heat spreader layers.

FIG. 6 depicts an example method for forming a backside heat spreaderlayer on a microelectronic device.

FIG. 7A and FIG. 7B depict another example method for forming a heatspreader layer on a microelectronic device.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

The following co-pending patent application is related and herebyincorporated by reference: U.S. patent application Ser. No. 14/499216.

The present invention is described with reference to the attachedfigures. The figures are not drawn to scale and they are provided merelyto illustrate the invention. Several aspects of the invention aredescribed below with reference to example applications for illustration.It should be understood that numerous specific details, relationships,and methods are set forth to provide an understanding of the invention.One skilled in the relevant art, however, will readily recognize thatthe invention can be practiced without one or more of the specificdetails or with other methods. In other instances, well-known structuresor operations are not shown in detail to avoid obscuring the invention.The present invention is not limited by the illustrated ordering of actsor events, as some acts may occur in different orders and/orconcurrently with other acts or events. Furthermore, not all illustratedacts or events are required to implement a methodology in accordancewith the present invention.

For the purposes of this disclosure, the term “microelectronic device”may refer to a semiconductor device, such as an integrated circuit or adiscrete semiconductor component, may refer to a semiconductor device ina wafer with other semiconductor devices, may refer to a semiconductordevice mounted on a substrate, may refer to a semiconductor device in apackage, and may refer to a semiconductor device encapsulated in anelectrically insulating material.

FIG. 1 is a cross section of an example microelectronic device with abackside heat spreader layer. The microelectronic device 100 includes asemiconductor device 102 having a front surface 104 and a back surface106. A component 108, such as a transistor, a diode, or a resistor, isformed in the semiconductor device 102 at the front surface 104. Thecomponent 108 may extend deep into the semiconductor device, possibly tothe back surface 106. A backside heat spreader layer 110 is formed atthe back surface 106 of the semiconductor device 102. The backside heatspreader layer 110 includes a heat spreader material 112 which may bepatterned as depicted in FIG. 1 or may be continuous. The heat spreadermaterial 112 is 100 nanometers to 3 microns thick, has an in-planethermal conductivity of at least 150 watts/meter-° K, and an electricalresistivity less than 100 micro-ohm-centimeters. The heat spreadermaterial 112 may include, for example, graphite, carbon nanotubes(CNTs), multiple layers of graphene, and/or boron nitride. The backsideheat spreader layer 110 may optionally include an adhesion layer 114between the heat spreader material 112 and the back surface 106 of thesemiconductor device 102. The adhesion layer 114 may include, forexample, titanium or titanium tungsten formed by sputtering, and mayreduce delamination of the heat spreader material 112. Other metals suchas nickel may be added to the adhesion layer 114 to improve subsequentformation of the heat spreader material 112. The backside heat spreaderlayer 110 may optionally include a cap layer 116 on the heat spreadermaterial 112 opposite from the back surface 106. The cap layer 116 mayinclude, for example titanium and titanium nitride, formed bysputtering, and may reduce delamination of the heat spreader material112.

The semiconductor device 102 is mounted on a substrate 118 whichincludes a header 120 containing fiber reinforced plastic (FRP), topleads 122 containing copper, vias 124 containing copper connected to thetop leads 122, bottom leads 126 containing copper connected to the vias124, and solder balls 128 connected to the bottom leads 126. Thesemiconductor device 102 is attached to the substrate 118 with anelectrically insulating die attach adhesive 130 such as epoxy whichattaches the backside heat spreader layer 110 to the top leads 122.Circuits in the semiconductor device 102 are connected to the top leads122 by wire bonds 132 at the front surface 104. During operation of themicroelectronic device 100, the component 108 may generate an undesiredamount of heat; the backside heat spreader layer 110 may conduct theheat away from the component 108 and so advantageously reduce atemperature rise in the component 108 compared to a similarmicroelectronic device with no backside heat spreader layer.

FIG. 2 is a cross section of another example microelectronic device witha backside heat spreader layer. The microelectronic device 200 includesa semiconductor device 202 having a front surface 204 and a back surface206. A component 208 is formed in the semiconductor device 202 at thefront surface 204. The component 208 may extend deep into thesemiconductor device, possibly to the back surface 206. A backside heatspreader layer 210 is formed at the back surface 206 of thesemiconductor device 202. The backside heat spreader layer 210 includesa heat spreader material 212 which may be continuous as depicted in FIG.2 or may be patterned. The heat spreader material 212 is 100 nanometersto 3 microns thick, has an in-plane thermal conductivity of at least 150watts/meter-° K, and an electrical resistivity less than 100micro-ohm-centimeters. In the instant example, the heat spreadermaterial 212 is electrically conductive and may include, for example,graphite, CNTs, and/or multiple layers of graphene. The backside heatspreader layer 210 may optionally include an adhesion layer 214 betweenthe heat spreader material 212 and the back surface 206 of thesemiconductor device 202, as described in reference to FIG. 1. Thebackside heat spreader layer 210 may optionally include a cap layer 216on the heat spreader material 212 opposite from the back surface 206.The cap layer 216 may include layers of copper and nickel.

The semiconductor device 202 is mounted on a grounded plate 220 of adual in-line package (DIP) 218. The semiconductor device 202 is attachedto the grounded plate 220 with an electrically conducting die attachmaterial 230 such as solder or silver-filled epoxy which attaches thebackside heat spreader layer 210 to the grounded plate 220. The DIP 218includes metal leads 222. Circuits in the semiconductor device 202 areconnected to the leads 222 by wire bonds 232 at the front surface 204.The microelectronic device includes a plastic electrically insulatingmaterial 234 which encapsulates the semiconductor device 202 and thegrounded plate 220 and holds the leads 222 in place. The microelectronicdevice 200 may accrue the same benefit from the backside heat spreaderlayer 210 as described in reference to FIG. 1.

FIG. 3 is a cross section of another example microelectronic device witha backside heat spreader layer. The microelectronic device 300 includesa semiconductor device 302 having a front surface 304 and a back surface306. A component 308 is formed in the semiconductor device 302 at thefront surface 304. The component 308 may extend deep into thesemiconductor device, possibly to the back surface 306.

A backside heat spreader layer 310 is formed at the back surface 306 ofthe semiconductor device 302. In the instant example, the backside heatspreader layer 310 includes a first heat spreader material 312 which ispatterned as depicted in FIG. 2. The first heat spreader material 312 is100 nanometers to 3 microns thick, has an in-plane thermal conductivityof at least 150 watts/meter-° K, and an electrical resistivity less than100 micro-ohm-centimeters. The first heat spreader material 312 mayinclude, for example, graphite, CNTs, multiple layers of graphene,and/or boron nitride. The backside heat spreader layer 310 mayoptionally include an adhesion layer 314 between the first heat spreadermaterial 312 and the back surface 306 of the semiconductor device 302,as described in reference to FIG. 1. The backside heat spreader layer310 may optionally include a first cap layer 316 on the first heatspreader material 312 opposite from the back surface 306. The first caplayer 316 may include titanium and titanium nitride. In the instantexample, the backside heat spreader layer 310 includes a second heatspreader material 336 at the back surface 306 on the first heat spreadermaterial 312, contacting the first cap layer 316 if present. The secondheat spreader material 336 is also 100 nanometers to 3 microns thick,has an in-plane thermal conductivity of at least 150 watts/meter-° K,and an electrical resistivity less than 100 micro-ohm-centimeters. Thesecond heat spreader material 336 may have a same composition as thefirst heat spreader material 312. The second heat spreader material 336fills the gaps between the first heat spreader material 312, and may bepatterned as depicted in FIG. 3 or may be continuous. The first caplayer 316 may provide adhesion for the second heat spreader material336. The backside heat spreader layer 310 may optionally include asecond cap layer 338 of titanium and titanium nitride.

Circuits in the semiconductor device 302 are bump bonded by solder bumps332 at the front surface 304 to top leads 322 of a substrate 318. Thesubstrate 318 includes a header 320 containing FRP; the top leads 322,bottom leads 326 connected to the top leads 322, and solder balls 328connected to the bottom leads 326. An optional potting compound 334 maybe applied to the semiconductor device 302, covering the backside heatspreader layer 310 and extending down to the substrate 318. Duringoperation of the microelectronic device 300, the backside heat spreaderlayer 310 may advantageously conduct heat away from the component 308.Forming the backside heat spreader layer 310 with the second heatspreader material 336 overlapping and extending across gaps in the firstheat spreader material 312 may advantageously reduce temperature risesin the component 308 compared to a segmented backside heat spreaderlayer having only one heat spreader material.

FIG. 4 is a cross section of another example microelectronic device witha backside heat spreader layer. The microelectronic device 400 includesa semiconductor device 402 having a front surface 404 and a back surface406. A component 408 is formed in the semiconductor device 402 at thefront surface 404. A backside heat spreader layer 410 is formed at theback surface 406 of the semiconductor device 402. In the instantexample, the backside heat spreader layer 410 includes a continuous heatspreader material 412. The heat spreader material 412 is 100 nanometersto 3 microns thick, has an in-plane thermal conductivity of at least 150watts/meter-° K, and an electrical resistivity less than 100micro-ohm-centimeters. The heat spreader material 412 may include, forexample, graphite, CNTs, multiple layers of graphene, and/or boronnitride. The backside heat spreader layer 410 may optionally include anadhesion layer 414 between the heat spreader material 412 and the backsurface 406 of the semiconductor device 402, as described in referenceto FIG. 1. The backside heat spreader layer 410 may optionally include afirst cap layer 416 on the heat spreader material 412 opposite from theback surface 406. The first cap layer 416 may include titanium andtitanium nitride.

Circuits in the semiconductor device 402 are bump bonded by solder bumps432 at the front surface 404 to top leads 422 of a substrate 418. Thesubstrate 418 includes a header 420 possibly containing FRP; the topleads 422 on the header 420, bottom leads 426 connected to the top leads422, and solder balls 428 connected to the bottom leads 426. An optionalpotting compound 434 may be applied to the semiconductor device 402,providing mechanical adhesion to the substrate 418.

In the instant example, a heatsink cap 440 is placed over the backsideheat spreader layer 410, covering the semiconductor device 402 andpossibly contacting the substrate 418 as depicted in FIG. 4. Theheatsink cap 440 may be metal such as stainless steel. The heatsink cap440 may be attached to the backside heat spreader layer 410 with athermally conductive material 442 such as a filled epoxy orsilicone-based heatsink compound.

During operation of the microelectronic device 400, the backside heatspreader layer 410 may advantageously conduct heat away from thecomponent 408 and into the heatsink cap 440 and so reduce temperaturerises in the component 408. The backside heat spreader layer 410 mayadvantageously improve heat transfer to the heatsink cap 440 compared toa microelectronic device with no backside heat spreader layer.

FIG. 5A through FIG. 5C depict an example process of formingmicroelectronic devices with backside heat spreader layers. Referring toFIG. 5A, a plurality of the microelectronic devices 500 are formedstarting with a device substrate 544 comprising semiconductor material,such as a silicon wafer 544. The device substrate 544 is processedthrough fabrication steps to form a plurality of semiconductor devices502 at a front surface 504 of the device substrate 544. Eachmicroelectronic device 500 includes a semiconductor device 502, and eachsemiconductor device 502 includes a component 508 at the front surface,possibly extending into the device substrate 544, possibly to a backsurface 506 of the device substrate 544. A continuous backside heatspreader layer 510 is formed at the back surface 506 of the devicesubstrate 544. The backside heat spreader layer 510 includes a heatspreader material 512. The heat spreader material 512 is 100 nanometersto 3 microns thick, has an in-plane thermal conductivity of at least 150watts/meter-° K, and an electrical resistivity less than 100micro-ohm-centimeters. The heat spreader material 512 is may include,for example, graphite, CNTs, multiple layers of graphene, and/or boronnitride. The backside heat spreader layer 510 may optionally include anadhesion layer 514 between the heat spreader material 512 and the backsurface 506 of the device substrate 544. Forming the backside heatspreader layer 510 across the back surface 506 of the plurality of thesemiconductor devices 502 may advantageously reduce fabrication cost andcomplexity for the microelectronic devices 500.

Referring to FIG. 5B, the backside heat spreader layer 510 patterned,for example by a mask and etch process. A spatial configuration of thepatterned backside heat spreader layer 510 may not necessarily coincidewith or be aligned to a spatial configuration of the semiconductordevices 502. Scribe lines 546 between the semiconductor devices 502 maybe designated for subsequently singulating the semiconductor devices502, for example by sawing or scribing. In an alternate version of theinstant example, the backside heat spreader layer 510 may not bepatterned, remaining as a continuous layer until subsequent singulation.Patterning the backside heat spreader layer 510 before singulating thedevice substrate 544 may advantageously reduce fabrication cost andcomplexity for the microelectronic devices 500.

Referring to FIG. 5C, the microelectronic devices 500 are separated bysingulating the device substrate 544 of FIG. 5B through the scribe lines546. Each microelectronic device 500 may be further assembled, forexample as described in reference to FIG. 1 through FIG. 4.

FIG. 6 depicts an example method for forming a backside heat spreaderlayer on a microelectronic device. A plurality of semiconductor devices602 of the microelectronic devices 600 is formed on one or more devicesubstrates 644. The device substrates 644 may be, for example,semiconductor wafers. Each semiconductor device 602 includes a componentformed at a front surface 604 of the corresponding device substrate 644.Each device substrate 644 has a back surface 606 opposite from the frontsurface 604. The device substrates 644 are placed in a depositionchamber 648 such as a furnace tube, so that the front surface 604 andthe back surface 606 of each device substrate 644 are exposed to anambient of the deposition chamber 648. Reactant gases such as methane,hydrogen and argon are introduced into the deposition chamber 648 andthe device substrates 644 are heated. RF power may possibly be appliedto form a plasma in the reactant gases. The reactant gases form a layerof heat spreader material 612 concurrently on the front surface 604 andthe back surface 606 of each device substrate 644. The device substrates644 are subsequently removed from the deposition chamber 648. The layerof heat spreader material 612 may be patterned on the back surface 606of each device substrate 644, for example as described in reference toFIG. 5A through FIG. 5C, to form backside heat spreader layers on themicroelectronic devices 600. The layer of heat spreader material 612 maybe patterned on the front surface 604 of each semiconductor device 602to form heat spreader layers which may advantageously reduce rises intemperature of the component, as described in the commonly assignedpatent application having patent application Ser. No. 14/499216, filedconcurrently with this application, which is incorporated herein byreference. Forming the layer of heat spreader material 612 concurrentlyon the front surface 604 and the back surface 606 may advantageouslyreduce fabrication cost and complexity of the microelectronic devices600.

FIG. 7A and FIG. 7B depict another example method for forming a heatspreader layer on a microelectronic device. Referring to FIG. 7A, aplurality of semiconductor devices 702 of the microelectronic devices700 is formed on a device substrate 744 which may be, for example, asemiconductor wafer. Each semiconductor device 702 includes a component708 formed at a front surface 704 of the device substrate 744. Eachdevice substrate 744 has a back surface 706 opposite from the frontsurface 704.

The device substrate 744 is placed in a spin-coating apparatus 750. Adispense apparatus 752 provides a CNT dispersion 754 onto the backsurface 706 of the device substrate 744. The CNT dispersion 754 includesCNTs dispersed in a solvent.

Referring to FIG. 7B, the device substrate 744 is placed in a bakechamber 756 which heats the device substrate 744 to 100° C. to 150° C.,for example using a radiant heater 758, so as to evaporate solvent 760from the CNT dispersion 754 of FIG. 7A to provide the backside heatspreader layer 710. The backside heat spreader layer 710 thus includesCNTs overlapping each other in a continuous layer, which advantageouslyprovides a high in-plane thermal conductivity. Forming the backside heatspreader layer 710 using the spin-coat process of FIG. 7A and FIG. 7Badvantageously reduces a thermal profile of the microelectronic devices700 and advantageously utilizes lower cost equipment compared to vacuumdeposition equipment.

While various embodiments of the present invention have been describedabove, it should be understood that they have been presented by way ofexample only and not limitation. Numerous changes to the disclosedembodiments can be made in accordance with the disclosure herein withoutdeparting from the spirit or scope of the invention. Thus, the breadthand scope of the present invention should not be limited by any of theabove described embodiments. Rather, the scope of the invention shouldbe defined in accordance with the following claims and theirequivalents.

What is claimed:
 1. A method of forming a microelectronic device,comprising the steps: providing a device substrate for a semiconductordevice of the microelectronic device, the device substrate having afront surface and a back surface; forming a component at the frontsurface; and forming a heat spreader material at the back surface toform a backside heat spreader layer, the heat spreader material being100 nanometers to 3microns thick, having an in-plane thermalconductivity of at least 150watts/meter-°K and an electrical resistivityof less than 100micro-ohm-centimeters, wherein forming the heat spreadermaterial comprises a plasma enhanced chemical vapor deposition (PECVD)process using methane and hydrogen to form a layer of graphite.
 2. Themethod of claim 1, wherein forming the heat spreader material comprisesboron nitride.
 3. The method of claim 1, comprising forming an adhesionlayer on the back surface, before forming the heat spreader material, sothat the heat spreader material is formed on the adhesion layer.
 4. Themethod of claim 1, comprising patterning the heat spreader material. 5.The method of claim 1, comprising forming a cap layer on the heatspreader material.
 6. The method of claim 1, comprising attaching thesemiconductor device to a substrate by forming a layer of die attachmaterial contacting the substrate and the backside heat spreader layer,and forming wire bond between the semiconductor device and thesubstrate.
 7. The method of claim 1, wherein the layer of die attachmaterial is electrically conductive.
 8. The method of claim 1,comprising attaching the semiconductor device to a substrate by forminga bump bonds at the front surface contacting the substrate and attachinga heat sink to the backside heat spreader layer.
 9. A method of forminga microelectronic device, comprising the steps: providing a devicesubstrate for a semiconductor device of the microelectronic device, thedevice substrate having a front surface and a back surface; forming acomponent at the front surface; and forming a heat spreader material atthe back surface to form a backside heat spreader layer, the heatspreader material being 100 nanometers to 3 microns thick, having anin-plane thermal conductivity of at least 150watts/meter-°K and anelectrical resistivity of less than 100micro-ohm-centimeters, whereinforming the heat spreader material comprises forming a layer of CNTdispersion comprising CNTs dispersed in a solvent on the back surfacefollowed by heating the device substrate to remove at least a portion ofthe solvent to form a layer of CNTs overlapping each other in acontinuous layer.